Filling up your tank in Indiana costs an average of 66 cents per gallon more than it did a year ago.

That's the highest year-over-year increase for gas prices in the nation, according to AAA.

The average price of gas has risen 18 cents per gallon over the last month to $2.84 a gallon, and it's climbed 19 cents per gallon over the past month to $3.06 in the greater Chicago metropolitan area. Neighboring Illinois' average gas prices has shot up by 62 cents per gallon, the fifth-highest amount in the country.

“Many motorists may have been surprised by the steady increases in prices at the pump this past month,” said AAA Chicago Director of Public Affairs Beth Mosher. “April brings a switchover to the summer blend of gasoline, which causes prices to rise. We expect prices to stabilize now leading into summer travel season.”

In Lake County, the average cost of self-serve regular unleaded gasoline stands at $2.74 a gallon, which is up 22 cents per gallon from the previous month and 34 cents per gallon from a year ago, according to AAA. Porter County's average gas price has risen 18 cents per gallon over the last month to $2.74 per gallon, which is 38 cents more than last year.

Midwestern states like Indiana, Illinois and Michigan have suffered some of the highest year-over-year gas price hikes in the country because their refineries recently switched over to the summer blend, which reduces emissions and improves air quality in congested urban areas but is more expensive to produce, Mosher said.

"The switch takes place all over the country, but not all at once," she said. "It's risen quite a bit over this past month. We haven't seen the peak yet, which traditionally occurs on the Fourth of July weekend, but it's tapering off a little bit."

Nationally, gas prices have risen 45 cents a gallon over the past year to $2.81 a gallon, according to AAA.

“If this past week’s moderate increases are any indicator of what’s to come, the fast rate at which gas prices were increasing may be slowing down,” AAA spokeswoman Jeanette Casselano said. “On the week, the national average held steady and 19 state averages remained flat or saw decreases in gas prices. Despite this stability, drivers on the West Coast and in Idaho, Utah and Pennsylvania are paying $3 per gallon.”

GasBuddy.com reports the average price of gas in the Gary metro area, which spans Lake, Porter, Jasper and Newton counties, stands at $2.86 a gallon, with $2.63 being the lowest price available at the 314 gas stations it tracks.

Gas prices have climbed to their highest point since November 2014, and this summer should be one of the priciest in recent years, said Patrick DeHaan, head of petroleum analysis for GasBuddy.

Refineries such as the BP Whiting have been humming along, so supply hasn't been an issue in the Great Lakes states. The 50,000-barrel-per-day Husky Refinery in Wisconsin that sustained an explosion last week is too small and too focused on heavy fuels like diesel for that disruption to put much of a dent in price, DeHaan said.

Prices at the pump largely have been climbing because of crude oil prices that have surged over $70 a barrel, the highest they've been in four years, DeHaan said.

U.S. output has been surging to the point where the United States should overtake Russia in oil production over the next few months, but that's unlikely to significantly lower prices because demand is high and supply is low, DeHaan said.

Customers may cut back on discretionary travel but relatively higher gas prices likely won't reduce consumption by more than 0.5 percent this summer, he said.

"It will be a minor impact," DeHaan said. "Demand is still very strong. Unemployment is low and people have jobs to get to. A lot of the demand is inelastic. People still need to get to work and the grocery store. If motorists really start to notice that it's over $3 a gallon for a long, sustained period of time, it could start to affect some discretionary trips, like vacations and going to see Grandma."

With so many geopolitical factors at play, such as Russia and Saudi Arabia wanting to lower inventories to prop up prices, it's hard to know where exactly gas prices will go from here, Luke Oil CEO Tom Collins Sr. said.

"Predictions are all over the place right now," he said. "At this juncture you could 'spin the wheel' and almost any answer you land on could be the right one."